This invention relates to a magnetron utilized in a microwave oven, defrosting machine or the like, and more particularly a magnetron having an improved strap ring secured to radial vanes.
As shown in FIGS. 1 and 2, a prior art magnetron comprises a cylindrical anode 1 made of copper, a plurality of copper radial vanes 2 secured to the inner wall of the anode and a strap ring 3 comprising inner and outer strap rings 3B and 3A respectively connected to alternate vanes by brazing 4 for short-circuiting interconnected vanes. At the center of the anode electrode 1 is positioned a cathode electrode 5 having a filament 5A. The opposite ends of the anode electrode 1 are hermetically sealed by end plates 6 and 7 to form an evacuated vessel.
When an electric power is applied to the magnetron, the filament 5A is heated to emit thermoelectrons which are accelerated by the electric field established between the anode and cathode electrodes 1 and 5 to interact with the magnetic field created by permanent magnets, not shown, whereby the electrons oscillate in an interaction space defined between the inner ends of the vanes and the cathode electrode to generate a high frequency electromagnetic wave. Finally, the electrons collide against the inner ends of the vanes to generate heat which is dissipated by the outer surface of the anode electrode 1 through the vanes. Accordingly, the temperature of the vanes 2 is higher than that of the anode electrode 1 and the vanes expand inwardly as shown by dotted lines shown in FIG. 3 due to thermal expansion. On the other hand, as the termperature rises, the strap ring 3 tends to expand outwardly. However, since the strapping 3 is soldered to the vanes, only the portions of the strap ring 3 between the soldered point to the vanes can expand outwardly as shown by dotted lines in FIG. 3. Consequently, large stresses are applied to the joints between the vanes and the strap ring. Accordingly, as the power ON-OFF of the magnetron is repeated, the application of the stresses is repeated causing rupture of the strap ring by fatigue, thereby shortening the life of the magnetron.